x t two-wire



Aug 24, 1943, Afw. DoNELsoN I 2,327,775

TWO-WIRE, TWO-WAY, LOCAL-CENTRAL STATION TRANSMISSION SYSTEM BY j n ML M. fro/z/vfs.

Patented Aug. Y y 1 i" i Y Arthur W. DopelsonfiniitMih.v ffl i Applicationrunee, 1942;,seia1'No. 446,125 l 1 (ci. '17e-t)V I A number. Thenthe desired'program isrsupplied Y irolaims. This invention relates to a two-way'electrical Vsifstembetwe'en a central station and a local stay tion, the central station beingoperatively asso: ciated with a plurality of local stations, the nurnl ber being determinablesolelyY by the number of central station operators and equipment, one central station operator usually being utilized in con#V nection with a plurality of local stations.

A.` system of this general character now in commercial use is commonly known as the automatic hostess phonograph'system, although the central station program supplied to the local stations need not be of lphonograph reproduced type.

Such systems require four transmission wires connecting each local vstationV to said central stations-` Y The chief object of the present invention `is to reduce the number of wire'srequired betweenV each local station and the central station.

Y Such reducti-on naturallyV is'less costly to install at theilocal station.

to the circuit vand 'reproducedat the reproducer` V VThe present invention is so arranged that vthe i :i depositors request is not reproduced at-the local station nor is the program reproducedatthercentral station.'v This' invention, [therefore '-elimi- Y nates the aforesaid undesirable features;

and operate, whether the wires bev cwnedior leased.V Further'such wire number reductions .y reduces the possible number of circuit variablesv v with all the attendant advantages. f The chief feature of 'the present invention is to provide in a system of the aforesaidv general char-p acterbut two wires between the central 'station rlhe full nature of lthe invention will be understood from the accompanying drawing andthe following description andclaimst- "In the drawing,v 7

Fig. 1 is Va' oiagrammaueillustration of :the in'- ventiong Vth eccin receiving station structure, -slug i ejector, coin registeringor lcounting device being omitted for clearn'ess andonly such portions of theseveral'output and input arrangements being shown as is necessary for an understanding of `the invention since theV remainder of such arrangements are ofconventional character.

'Figi 2 is a vvdiagram of a modification of a lpor-- ti'on'o'f the local'rstation circuits-i as hereinafter specified. y y Y p Eig. 3 is a diagram of a modification of a` portionloffthe centralistation circuitsas hereinafter and the local station andto utilize at both `sta-f` j tions certain arrangements which permit satis-f factory utilization of such twoewires, Sucharrangements being mutually cooperative; For a better understanding of the present-im vention some general description is believed in* order, and referring to `such liostesssystem',j at each local station, there isamusic reproducing arrangement which has one or more coin receivl ers. At each coin receiving station there visineluded a switch that closesV a circuitwherr theV proper coin has been deposited and has "beenac-J'- knowledged to be proper if a coin'selector' is utilized and the circuit so completed includes a; coin controlled coill relay. f i

'To keep a financial record of the money deposited at anyone local v.station there is associated with the singular pair of lines in the central station a personal Acoin counter circuit which includes'a conventional coin counter relayV that controls a switch in a circuit `to a counting device which may be of any one of the conventional types now known. L The coin operable relay at the local station-when actuated thus registers coin deposition in the centralstation.V

The central station operator then depresses the operators key in' the'proper circuit and requests the depositor' to designatethe desired program amount of Before proceeding withV adetailed description ofthe invention reference will rst be had to the coinl controlled-'circuit and the coin registering circuit.` In the drawing AiandlB designatetwol lines between Ya localstation? and a central station., At the local station there is included at Vleast one coin operable switch diagrammatically in seriesirwith a coin operable relay Ill, the movable portion Illa ofwhich is associated withcertainswitches. i

At the central station is a counting device, not

shown, that is Yelectrically operable, the supply to theioperatin'g circuit therefor also being' omit-` ted, said circuit including line I3 and a switch l-2 operable by a relay Il having movable por? tion lla.Y The switch' l2 includesV stationary contact 12b and movable contactlZa both in the circuit including 1in`ei|3. switch 2 is normally open. `When closed byrmernber Ila in response to relay Il enrgization, the coin register-lis actuated f .Y

,V `Relayfll '-is `connected by line I9 to line A.

Itis alsoconnected toline B by line 2i). Across I Vthe relay VH and in" multiple therewith there i 'may' be includedthe resistor Rand in series With the condenserl 22 for reducing` orlirniting Y 'The coin controlled: relayi lll moves member lila.` AssociatedY therewith are three switchesy designated by numerals I4, I5 and I6.

Yby experiment.-

leg -Zfand line 3l a-t 39 as illustrated.

The switch I4 is a'member responsive to coin relay I and it is 4normally in Contact with switch point I4a for closing the line A.' The switch I5 is normally in Contact with. the switch point |511 for normally vclosing the line B. There is a lpair ofsupplementary supply lines Il and I8 connected toA a loW voltage supply, herein 25 vvolts A; C. Line 'Il therefrom leads toa switch V`point I'Ia. while lineIS leads to a switch point I8a. When the coin relay I0 is energizedby coin deposition, the switch points I4 and I5 are moved by member Iafrom the contacts 14a and.y Iot,v respectively, to engage the 1 contacts I'Ia.

and Itri,A respectively, thereby supplying voltage to the lines YA and B from the local stationito the central station including lines: 'IST and 25.1,"1 "j before mentioned,

for coin registrationk at the central station.

current supplied from lines "I 'I` and` I 8, v the fswitch l Ymernloerjl I2a moves tolcontactcontact lilly.'A fait will Vlcj=yyn`tegi 'this` central. stationswitch,v t? is normally open andis only closed vwhen the coin spssitsd ai theA locslststion `-Ti1s. stilistica device thereupon isienergized by the circuitconnectelA thereto andcontrolled bythis switch- I2, which. countingfdevice is at the central-station so that the central station has a nancialrecord of thecoins deposited at the local station and i Atthe local stationtherevis.- provided a micros phone.; preamplifier output trsnsfarmsr. 2?. ,which Couplesths; Output' 0f. the misrophone, p.rean'1ri1i.;y 'ler -toz alternate, legs of a Wheatstonel bridgei There is also` al -tranjs-fonnerY 24vI which couplesv the other. alternate terminals of'l the. Wheatstone bridge to the; inputfoi the program amplifier The Wlieatstane bridge. includes either two 500 ohms resistances and 1,000 ohn1sp otenfk tiometer -or two13000 ohms,- potentiometers which arrangedysttst they. are; balancear Wheatstone bridge arrangement includelsnaleg kW and: les. The-131GB issonne'ted. tov the junction; or; t'stnsirialA of; less. W.:v and; Xgiatii,

- Arossiihe. issX; is interposedfa condensen 2.6;

the value of which isunknown andis determined mined by; thedielectriccapacity of the two lilies tOtWhiChit is s111111.estad.;k f

The vthird les: O ff the.

these two legs is connected by line 28 to one end 0f the:v secondary .23;brof; the transformer, V'23. The otherf end of this secondaryy is connected Y 1 52o When the coinV isI deposited at-,thelocallstation A and-.by ,reason of. energization Vof coilv I.I yby the This.` isfimdamentally. deter;-VV

by the" line 2,3 to thedline- B The linegAf` con.-

115115.21@ 3.0 't0 th@ leg Wi Theflie. 3 from the."

les, X Connects mths.. other end .0fthsflsg Z@ The line 32 fromthe other. endof. leg Y connects tothe line Ajfat, 38fby'line 33 to Y'one'terminal of the primaryla of the program inputtransformer.24,` The'otheij terminal thereof is connected by line` 34 to 'the In addition to the foregoing, a line 35-"isjco n nected-` at 38 tothe 'line vi23 andit-fincludes the y coin operable movablenswitchsmemberI6, before` l mentioned.; Associatedstherewithis a stationary contact Iawhich .isconnected :by the line. 35`1-to Vlixjiejfl at 3l, onl'the side-of; switch. I5; remote from the central station. When the coin is,;def lwiedirisofsrgas switch.- i';.is.-..sQr19eri-ie1; switch The line A is connected. atn

'zgzvzvsf i t member I6 closes a circuit fromline B'if switclif I5 contacts contact I5a vand the effect of the closing of switch I6 is to short'out the'secondary of the transformer 23. The relationship ofthev several switches I4 I5I6 is as follows:

Switch member I6 must make Contact withy contact ISa before switch members I4 and` I5 break from contacts I4a and I5a, respectively.

In returning to normal theswitch member VI5 must break contact from Ita. after switchpoints I4V and I5 have made contact with contacts I'4a I i and E511, respectively. The reason for this stipulation is that unbalance caused by the removal Y ofi lines shall;n ot cause acoustic feed back which 1551.V

-of the. path of possible 'acoustic feed back,v or

isv accomplished by interrupting the continuity oscillation;` Y

The Y foregoingv 'constitutes a description of substantianyan that is found and-required at therlocalV station, and theY local station registrationinthe centralofiice or-station i At the central stationY there is provideda transformer-40 whiohlhasrits seoondaryA(Ibconnected tothe operators.receiverinput arrangementpinfg cluding a tube hl with afgrid 19a. i There :.i'salsrV provided at the central Vstation.another transe;

former-4 I the l primaryd Ia ofA which iszy conn@ctetiv to the program outputandj the operators micros Y phoneo-utput arrangement,j includingv atube-.Blf

with a plate 60a,- ThelinefA connects at42jtqf v primary '49a of; the transf-. former Ihe line B connects ati-43f-to-.one Y. minal of the secondary4Ib--of-theftransformegug Y The transformen 4I is subrstantially` the output I one terminal of the transformer of the :programpreamplifier? Tfransf: former 40 is the input transformer of the-lopez ators-receiveliamplien Y theY secondary 41th of;l the: transformer Ytls-tdI one.r leg-designated by theletter-li/I of.l the-Wheat and attrito the-Jinete;

stone bridge atthe central stat-ion, has butifthreq 'i le'ssthe-repi -loatedfati.thatstation; Thef'fourth I les Off. this-bridge; in-ithis instance, is the legw at the, 10mi-station. "if desired-thema Wv-ml'am.

be. connected -acrossflines-v A Land B 'atrtheg Central.; f f station and-:iii that; Y Vent lee--wfwouldxbazomitted atthe lssalfstatioit A further, mosicatioii weuldfbetQ-hav'e that@ W twice the, valuey Qf-iisaorginall valueffandgloe catedjatjheL-looal station-as shcwn; anday anjotlieny q leg of i the same value, that-is(twice.Y theevalueioir. Y

the leg W, at the 4centraligstation,, gth'e;latteryfleg thsnbsine soniissted across fthe-f lines4 A1 andBL. The; resulting effect since these.; two; legs are-.-in

parallel; W011ld-be;thtithese: two-legs.. although;

each arezofdoilble valu.. in electrical,effect;v1/,omc

hsvethessmegvalue sthezsinaular;-1egW,zposi+. tionedzat; eitherthef-lacal station-ori the; 'cent-m1, f

static v Itis '.eresiwith1=this descrittioni:notillustraJ tioniof.. bese two-madiicationsisarequiredr.x 1.15' f thi. the; same; the

.entralstationless Ceiizlton it istil.befobserved-Ltl precaution i as. to values with; .regards I NlfandiRmusttbesohe' 'servedfthatfhaye bccmmntionew imclonnectiw `with'the values of the localfstation'legs-l/V, XgiY and Z. -In other words, balance must be main# tained. l Y In this connection it contact 25 between the legsW and X is'inten'- is also' to be noted theV tionally madeA variable to compensatefor the'V resistance of lines A and B whichmay vary." f-

Any modulation appearing across thesecondari/23a of transformer 23 appears across points 25 and 2'! of theWheatstone bridgeat-the local i station and since `the bridge v is'balani'sedthis modulation will'lnot appear across the primary 24a of transformer 24 which isV connected be-f tween points Sl'andtlg` The modulation, nhow; ever, will appear across leg W and be'convey'edf by means of lines A and Btc points 46A and 50 whereupon said modulation' will occur in both transformers 4D and 4|. y l

The modulationl set up Vin the secondary-Mb oir` transformer 4I will be to no avail for the primary Ma thereof connects to -the platerlla of, the tube 60 which is unresponsive to this modulation.

,Howeven the modulation set upin the Vprimary 40a of transformer Ell willY appear in the sec-A ondary liilb thereof and effect the gridzla of tube 1B, thereby conveying the modulation-from the microphone preampliiieroutput at' theloc'al station to the operators receiver input.' f

In a likel manner, modulationintroduced into` the primary Ma of 'transformerl by the plate 6ta of tube 60 willvappearin secondary 'Mb and in leg N between points 5,2and Eil, same being alternate leg terminals." This modulation is ,not

received atpoints. i6 and 5i,-the other alternateA leg terminals of the central station bridge, dueto the balance of this circuit, butthat modulation is conveyed by lines A ,andV B `to pointsil and 25 across one legW ofthe localstation bridge, which is conveyed 'to the circuit, .as il-VV lustrated, to thelsecondary 23h` of transformer 23 and tofthe primary 24a of transformer24.

The modulation thus introduced. into the primary 23aof transformer 23 is of no avail for it appears on the plate 80a of,l tube SEB, which is y,

unresponsive to such modulation. The modulation occurring across the primary 24a oftrans.- formerr appears in secondary Mb thereof and 'elects vthe grid Slaoi tube 90 causing the signal or modulation which was introduced from the plate Killa of tubell at the central station to Vbe introduced intothe program ampliiier at the local station. Y g

It'will be noted that any modulation or signal introduced into the system fromV the tube 86 is not reproduced by the tube GOVbutvis reproduced by the tube 10 and it will also be noted that any signal, etc., introduced by the tube 8i) is not reproduced through the tube 9B.

In like manner any signal introduced by the" tube E0 is not Vreproduced bythe tube 80 but isv reproduced by the tube 90 and similarly, that rather location shown; becausei't 'may be intro#- ducedfat-other points inthe ci'rcuitto' render either the microphone amplifier circuit orthe `program amplifier circuit inoperative for'the purpose set forth, to-wit, elimination of oscillation Y, Referring to Fig. Zand Fig; 1, nnote that be tweenrpoi'nts 25 and `3l] of the latter there mayV be connected in multiple with 4leg'Xfat the local w station, a conventional impedance network designed to match the alternatingV current irnvpedance imposed between points 25 and 30. In

this case (lig.` 2) each resistance has a value of fone-half the total ofthe line resistance, the condenser has a capacitance equal to the capacity between line wires'A and B andthe inductaneel shown in Fig. 2 electrically matches that of re- The purpose of the -1 Aaforesaid is to maintain balance through the lay l l Y winding-see Fig. V1.

audio spectrum.

Referring to Fig'. '3 and-Fig. 'l note that between points 45 and 5B there may be included in place of or in multiple vwith leg M orl N at the central station a conventional impedance network designed to matchthe alternating Ycurrent impedance imposed between points 46 and 50-` seeFig. l-the purpose o`f which is to maintainVv continuous balance throughout theaudio spectrum. v Note herein there is illustrated, compared withFig. 2, an additional 500 ohmresis'tance.V The other units have the values speciiied above relative to the units illustrated in' Fig. 2:

y While'the inventionfhasV been illustrated'and described in great detail in the .'drawing and foregoing description, the'same is to be considered as character.V

The several modifications described herein as well as others whichrwill-readily Vsuggest vthemselves to persons skilled einY this art, all are considered to be withinthe broad scope of the in-`` vention, reference beinghad to the appended claims. Y

The invention claimedis:V Y i l. A system -including'a local station fand a central station and but two wires therebetween; an operators receiver input structurek at the central station, including a tube with a grid therein, and an operators microphone and program output structure at the central station, including a tube with a plate therein, said structures each including a transformer coupling to said wires,

a Wheatstone bridge structure operatively inter-l posed between said wires and structures, a program inputstructure at the local station, including a tube with a grid therein, a microphone preamplifying output structure at the local station, including a tube with a plate therein, said two last mentioned structures each including a transformer coupling to said wires, and a Wheatstone bridge structure operatively interposed between said wires andY the two last mentioned transformer coupled structures, the legs of each bridge being balanced.

l 2. A system as defined by claim 1, characterized by oneleg of one bridge serving as a leg of the otherl bridge and being positioned at one station. 3. A system as defined by claim 1, characterized by each bridge having a leg double the value of each of the other legs, the double valued legs being connected in multiple across the wires.

4. A circuit of the character described including a local station including a program input device and a microphone output device,- a centhe' swan-1 le is iiiustr'ated mi thefrpositi 'orf illustrative andv not restrictive in ing-a common lee-.

traiY sta-tiem including. a; program output'fdevice'f an n operators' receiving inputidevice; aj singlef lpair of wires-i therebetween;- f and 'arW-heatstoner bridge arrangement for:.eactrstation:` Y

J circuitofvthe; character.` described .incl'ijid` ingla-localistaticrr :includingga programvv` input device and a microphone output device-g-aqcentrali arrangementi for.. each station.,` said stations hav-j S. A1 systemf; as:v deined l'flyfclainiie,y character-V A izedfvbyg the addition cfaI coin registering device-` operating circuitiat the' central station', localI station coin controlled circuit, a supplementary soul;ce-, ofy energy si-ipply, switchV means at the? local 'station arranged to-open `the pairiwirecon;

Vnecticms;,to. the; local stationj structures and' conneet tlfiefliair'v of 1wires to thesupplementary; supe-- ply, and means at the central station `responsive only toythat 'supply and controllingl theregistering device.f-operating;k circuit foroperation` upon coin dcpositionfsat Ytherlocal station. j Y 7. Assystemas denedby claim 4, character-fj ized. bythe addition of a.-coin Yregistering device Operating circuit at the-central station, a local station. l. coin f controlled circuit, 4,asupplementary source of@ energy snpply,-Z switch -means at the localstation. arranged to open the pair wire connections to thelocalstation g structures andl con` nect the pairot wires to theA supplernentarysup-v i ply, means atf theV central stationeresponsive only Y to..that supply;V and. ,controlling the registering device-operating circuitgfo'roperation fupon. coin :y

de'eposition.at..t1f1e local fstation, a transformer'.

Ycoupling v-eaclfr-device across -thewires, a; normally.:

open circuit across one of the `transformer'l cou-Y plingstand switch means -infsaidy last mentioned circuito-rA shortingi-o-utsaid coupling and re;v

i spensive toa coin controlled` circuit operation and:

inpredet'ermined timedY relation to locallstat-ion'.

Y switchfmeans operation;

3. A system including at one station a priillary` and a secondary of two transformers, another stationincludingfa primary and-aseccndary of two other. transformers, f the l pri-mary at one station asa-nrw s l beirgconnectedftoftheseccndaryfatthe other stair tion;i a pair, of wires'.f only.l betweenf; stationsygc vWheatstone bridge at each station and operatiyely.'

interposed between vthe wire connections-to said transformerslofl said: stationsnoneleg'ofcaich: .Y :bridge being in? series with-4 one .portion'iofv a-i- 'transformer' at thaitvstation', AsaidI e'gVan-c1:trangsfi former portion being across. said Wires, and an alternateleg of the"sarn'e"br dge being in series withA the other portion-,oi theotherl'transformcrat p thelfsamer-station;L saidalternatelegandc'othei? the pair of wires to thersupplementary-fsupply, and'meansat -the central station responsive-only to'lthatjsupply andcontrollingtheregisterin'gf dee;

. vicev operating.' circuit l forv operation uponf comf deposition. at the vlocal station@ ized. by; the addition ofva coin-'registering device;

operatingv circuitat fthe central stations aflocal. station vcoin l cont-rolledv circuit,- ai supplementary@ sourceo` energy supplyggswitcl-rmea-,ns ate-the? v local station-arranged to;open,thefpairrv/ire'con#k j Y nections to the; local'y station structures'and-connectvthefpair of-Lw-ires to the supplementary. supgj ply;V means atv the central station-:responsiveonly-'r to that Isupply-fand controlling the-registeringsdew I, vice operating circuit: Yfor o-peratiorruponcoin;`

' deposition at the llocal station, a' :normally open` circuit across-one portion of-'a -tlansformerfandi' switch means; in said last mentionedfcircuit ifor;`

shorting:out the.l'astmentionedtransformerpor1 tiorii'and responsive to coincontrolled: circuit op eration and'-in predetermined: timed frela'tiont local st'ationjswi-toh-means operation. Y 11.5 Arsystemasfdnedby claim 85de?hairzicterl"y 

